An ADM terminates a synchronous transport signal (STS) path signal or a virtual tributary (VT) path signal and performs several other important functions. One of these functions is the received path trace detection function.
The received path trace detection function is generally called the “path trace identifier mismatch detection function” and is usually abbreviated as “TIM detection”. Note that this abbreviation will be used in the later explanation of the present invention as well.
This TIM is detected when a TIM defect occurs. Here, a “TIM defect” means the state of erroneous path connection (connectivity defect) where a “path terminal equipment (PTE) at a certain network element (NE) ends up being connected to an erroneous far end PTE through the network” due to the network manager (user) mistakenly setting the path when the user sets up the path in the network. This TIM defect is an important alarm (ALM) in the various ALMs issued by an ADM.
Specifically, in the above ADM, a path trace detection apparatus receives a string of a path trace signal (path trace string) continuously sent from the PTE to detects the received path trace, while an associated erroneous connection decision unit (CPU) decides whether “the values exhibited by the string of the path trace signal and the expected values preset by the user mismatch” and issues the above ALM. When this ALM is notified to the user, the user learns that the preset path is erroneously connected and immediately resets to the correct path.
Here, this string of the path trace signal is for example a string of 64 bytes of a signal in a synchronous optical network (SONET) or a string of 16 bytes of a signal in a synchronous digital hierarchy (SDH).
Note that at the present time, the above TIM defect (and TIM failure) is defined only with respect to a STS path layer, but in the future it is expected that it will be defined for a VT path layer as well (with respect to a VT section layer as well). Below, when it is necessary to differentiate between the STS and VT, a TIM defect of the STS path layer will be expressed as “TIM-P” and a TIM defect of the VT path layer will be expressed as “TIM-V”.
At the STS path layer, the above string of the path trace signal is a string of J1 bytes (64 bytes' worth), while at the VT path layer, the above string of the path trace signal is a string of J2 bytes. As is well known, a “J1 byte” is a byte mapped in the STS path overhead, while a “J2 byte” is a byte mapped in the VT path overhead.
Note that in the present invention, in addition to the above received path trace detection function, the function of monitoring for bit error included in a path signal for improving the reliability of the ADM will also be alluded to.
After this, as explained in detail with reference to FIG. 23 and FIG. 24, in a received path trace detection apparatus in a conventional ADM, there was the problem that it was not possible to most quickly handle the recent diversification of networks, diversification of types of services, and demands for increasing the number of channels serviced by systems.
Further, there was the problem that the bit error monitoring function in the ADM had to be further improved.